installation of underground
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Installation of UndergroundInstallation of Underground
Services using HDD:Services using HDD:Design ConsiderationsDesign Considerations
By Dr. Samuel T. Ariaratnam, Ph.D., P.Eng.
Arizona State University, USA
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HDD Installation ProcessHDD Installation Process
Pilot Bore Phase
Pullback Phase
Typical Reamers
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Bore Path PlanBore Path Plan should show:
the surface grade line
locations of important surface features
anticipated lateral utility connections and
intersection points
bore depth at each reference point and at critical
points
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Bore Path SelectionBore Path Selection in agreement with:
geometric restrictions and/or requirements
topography
geology
site-specific issues
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Designed Bore ProfileDesigned Bore Profile
recommended:at least one complete length of drill pipe beforestarting to level out the bore path
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BoreplanningBoreplanning SoftwareSoftware
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Entry and Exit AngleEntry and Exit Angle entry angle :
8-16 degrees
determines a set-backdistance of the
machine
exit angle:
5-10 degrees
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Recommended Relationship betweenRecommended Relationship between
Product Diameter and Reamed DiameterProduct Diameter and Reamed Diameter
Diameter of product + 12> 24
Diameter of product x 1.58 24
Diameter of product + 4< 8
Reamed DiameterProduct
Diameter
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Design AspectsDesign Aspects
Essential for successful installation
Allows suitable alignment selection
Can define installation procedures( buoyancy control)
Determines Suitable Equipment Selection
Minimizes Pipe Failure
During Installation
Long term operational (bending)
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BackgroundBackground
Two Publications
Installation Loading and Stress Analysis
Involved with Pipelines Installed by
Horizontal Directional Drilling Form basis of American Gas Association
design guidelines for HDD
Polyethylene Pipe for HorizontalDirectional Drilling
Developed by the Plastic Pipe Institute for
design of HDPE for HDD
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Pipe MaterialPipe Material
Steel Linear Elastic Material
High Tensile strength
High modulus of Elasticity
Large Diameters (>24) except for casings Corrosion and Abrasion Typically Required
High Density Polyethylene Viscoelastic material
Tensile stress & Modulus of Elasticity time,temperature, andduration dependent
Higher resistance to short term loading than long term loading
Duration of loads needs to be considered
Low Modulus of Elasticity & Tensile Stress
5% strain level to prevent long term structural damage
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SOIL COMPARISONSSOIL COMPARISONS
FOR 8 HDPE DR17FOR 8 HDPE DR17
-0.20
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
0 10 20 30 40 50 60
Bore Path Location (m)
Strain(%)
Clay 1
Clay 2
Sand
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HDPEHDPE
Typical Apparent Modulus of Elasticity (E) Typical Safe Pull Stress
Duration HDPE MDPE Duration HDPE MDPE
Short-term 110,000 psi(800 Mpa)
87,000 psi(600 Mpa)
30 min 1,300 psi(9.0 Mpa)
1,000 psi(6.9 Mpa)
10 hours57,500 psi
(400 Mpa)
43,500 psi
(300 Mpa)60 min
1,200 psi
(8.3 Mpa)
900 psi
(6.2 Mpa)
100 hours51,200 psi
(350 Mpa)
36,200 psi
(250 Mpa)12 hours
1,150 psi
(7.9 Mpa)
850 psi
(5.9 Mpa)
50 years28,200 psi
(200 Mpa)
21,700 psi
(150 Mpa)
24 hours1,100 psi
(7.6 Mpa)
800 psi
(5.5 Mpa)
Apparent Modulus of Elasticity and safe Pull Tensile Stress @ 73oF
(Plastic Pipe Institute, August 1998)
Steel? Modulus of Elasticity = 2.9 X 10
7 psi
? Safe Minimum Yield Strength 30,000 to 50,000 psi
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Pipe Capacity ComparisonPipe Capacity Comparison
SteelSteel
O.D. = 14O.D. = 14
w.t. = 0.25w.t. = 0.25I.D. = 14 - 2(0.25 ) = 13.5I.D. = 14 - 2(0.25 ) = 13.5
O.D. = 14 DR 17O.D. = 14 DR 17
w.t. = 0.82w.t. = 0.82I.D. = 14 - 2(0.82 ) = 12.36I.D. = 14 - 2(0.82 ) = 12.36
HDPEHDPE
Allowable Pull LoadAllowable Pull Load Allowable Pull LoadAllowable Pull Load
= 40,700 lbs= 40,700 lbs
= ( 14= ( 1422 - 12.36- 12.3622 ) 1200psi) 1200psi??44
= 324,000 lbs= 324,000 lbs
= ( 14= ( 1422 - 13.5- 13.522 ) 30,000psi) 30,000psi??44
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Installation Loads andInstallation Loads and
StressesStresses Two Phases
1) Installation
2) Operation
Installation usually governs except inhigh operation pressure conditions
Deep Installation can limit HDPEinstallations
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Installation LoadsInstallation Loads Tension
Frictional Drag
Fluidic Drag Unbalanced Gravity Effects
Bending
External Hoop
Pipe Support Spanning
Pipe Overbend at Entry
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KEY STRESS AREASKEY STRESS AREAS
DURING PULLBACKDURING PULLBACK
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OperationalOperational Conduit Pressure/Vacuum
Ground Water/ Soil Pressure Key Assumption Stable/Unstable borehole
Live Loads -H2O, Coopers, E80,
nearby structures
Generally small at depths greater than 5 - 10
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Stable boreholes, no side support
Unstable borehole Pipe Arching
GROUNDWATER GROUNDWATER
STABLE BOREHOLE
BOREHOLE
DEFORMATION
SLURRY SLURRY
Borehole DeformationBorehole Deformation(Plastic Pipe Institute, Aug. 1991)(Plastic Pipe Institute, Aug. 1991)
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1 DAY 1 WEEK
2 WEEKS 4 WEEKS
8 HDPE Pipe8 HDPE Pipe
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1 DAY 1 WEEK
2 WEEKS 4 WEEKS
8 HDPE Pipe8 HDPE Pipe
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Summary of 1 Year Digups 8 PipeSummary of 1 Year Digups 8 Pipe
Clay
Sand
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Load CalculationsLoad Calculations
Crossing broken down into straight
line and curved sections.
Loads Determined for:
Net External Loads
Pipe Deflection Unconstrained Buckling
Pullback forces, (Friction, Fluidic,
bending, unbalanced gravity)
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FFTOTALTOTAL = T= TAA + T+ TBB + T+ TCC + T+ TDD + T+ TEE + T+ TFF
Horizontal Directional Drill ProfileHorizontal Directional Drill Profile(Huey et al, 1996)(Huey et al, 1996)
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Net External LoadsNet External Loads Stable Borehole
PNET = PMUD - PI
Unstable BoreholePNET = PE + PGW + PLIVE - PI
P = H
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Pipe DeflectionPipe Deflection
Buoyancy
Earth Load
For HDPE pipe, care needs to be utilized onselecting an appropriate E. Conservative islong term values.
Deflection generally minor on steel pipe
4
=EI
0.1169
2
D
D
3
=E
0.0125 PE
D
12 (DR-1)
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Unconstrained BucklingUnconstrained Buckling
Uniform external pressure results incompressive hoop stress
For HDPE
For Steel
fo = ovality factor (0.4 for 7.5% deflection)
fr = tensile reduction factor
if pipe is constrained by soil or grout fr is replaced by
fs (grout enhancement factor) which is approximately 5 for grout
? = Poissons ratio
D
tPALLOW = 0.88 E
2
2t
Pnet Dfn =
DR-1
1PALLOW =(1 - u2 )
2Efo fr
3
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Buckling for HDPEBuckling for HDPE
During PullbackDuring Pullback
14 HDPE DR 17
= 9.8 psi
17-1
1PALLOW =
( 1 - 0.352 )
2 ( 55,000psi )(0.4) (0.8)
3
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P = h
= 17.5ft of drilling fluid head
if water utilized to counteract external pressure
h =P
=9.8psi ( 144 )in2
80 lbs ft3
ft2
h =9.8psi ( 144 )in2
80 - 62.4
ft2= 80ft
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Pull Back ForcePull Back Force
Main component is pullback forces
Determined in straight line and
curved sections
Consists of:Friction
FluidicUnbalanced Gravity
Bending
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Straight Section ModelStraight Section Model(Huey et al, 1996)(Huey et al, 1996)
T1
T2
N2DRAG
L
frict
0
WsL
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Pull Back ComponentsPull Back Components
Buoyancy has significant effect on Ws
0.25 - 0.40usoil
FTOTAL = Ffrict + Fdrag + Ws L Sin 0
Unbalanced Weight EffectsFweight = Ws Sin 0 L* *
?
Fluidic Drag
Fdrag = 12 D L umud* * * *
* * Friction
Ffrict = Ws L Cos ? usoil*
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Buoyancy EffectsBuoyancy Effects
No buoyancyNo buoyancy
Pipe WeightPipe Weight = 14.9 lbs / ft= 14.9 lbs / ft
NET ( Ws )NET ( Ws ) = 70.6 lbs / ft= 70.6 lbs / ft
14 DR 17 HDPE14 DR 17 HDPE
Weight = 14.9 lbs / ftWeight = 14.9 lbs / ft Mud Weight =Mud Weight = mudmud = 80 lbs / ft= 80 lbs / ft
33
== 85.585.5 lbslbs/ ft/ ftBuoyancyBuoyancy == mudmud = ( )2 80 lbslbs / ft/ ft 23
??
44
12121414DD2
?
44
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Buoyancy - Water Utilized in PipeBuoyancy - Water Utilized in Pipe
For 400 ft BoreFor 400 ft Bore
85.5 - 14.9 - 52.085.5 - 14.9 - 52.0 = 18.6 lbs / ft= 18.6 lbs / ftNET ( Ws ) =NET ( Ws ) =
14 DR 17 HDPE I.D. = 12.3614 DR 17 HDPE I.D. = 12.36
(( ))22 62.462.4 lbslbs / ft/ ft33??
441212
12.3612.36 = 52.0 lbs / ft= 52.0 lbs / ftWeight of Water =Weight of Water =
F no buoyancy =F no buoyancy = ( 70.6 lbs / ft )( 400 ft )( 0.3 )( 70.6 lbs / ft )( 400 ft )( 0.3 ) = 8,470 lbs= 8,470 lbs
F buoyancy =F buoyancy = ( 18.6 lbs / ft )( 400 ft )( 0.3 )( 18.6 lbs / ft )( 400 ft )( 0.3 ) = 2,230 lbs= 2,230 lbs
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T1
N
N2
N1
WsL
frict
frict2
frict1DRAG
01
02
a
R
Curved Section ModelCurved Section Model(Huey et al, 1996)(Huey et al, 1996)
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BendingBending Steel
Modelled as 3 point bending and is complex
and iterative
HDPE
Not an issue as safe bending stress (?40D) is
much less than typical drill curve radii of 300
ft or more (i.e. drill rod limiting)
Forces calculated using cable laying formula
Fcurve = e?? (? soilWBL)
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Stress AnalysisStress Analysis Once all loads are calculated, stress
analysis is undertaken to ensure allowable
stresses are not exceeded.
Highest stress will typically occur wherebending, tension and external/internalpressure act together.
Loads to be looked at individually and incombination.
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Effect of CollapsedEffect of Collapsed
Borehole on Pipe FrictionBorehole on Pipe Frictionand Loadand Load
GROUNDWATER GROUNDWATER
STABLE BOREHOLEBOREHOLE
DEFORMATION
SLURRY SLURRY
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Stable BoreholeStable Borehole
F frict = Ws L Cos ?? soil
= (70.6 lbs)(400 ft)(0.3) =8,470 lbs
F drag = 12? D L ? mud
= 12? (14 )(400 ft)(0.05) =10,555 lbs
F total = 8,470 + 10,555= 19,000 lbs
Ffrict
Fdrag
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Unstable BoreholeUnstable Borehole
Assume 30% of length collapse
Frict = (70.6 lbs)(280 ft)(0.3) =5,930 lbs
F drag,collapse = 12? (14 )(120 ft )(0.3) =19,000 lbs
F drag = 12? (14 )(280 ft)(0.05) =7,390 lbs
F total = 32,320 lbs
Frict
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Always Have A Plan!Always Have A Plan!
Contractors
Contingency Plan
Engineers Plans
and Specs
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Bore Tracking and EquipmentBore Tracking and Equipment
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IntroductionIntroduction Two categories of tracking methods
Walkover systems
Non-walkover systems
Operate best in interference-free environment
(active vs. passive interference)
Drill locator is responsible for ensuring that thebore follows the design profile
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InterferenceInterference A log book containing drill pipe number,
pitch, depth, steering commands, apparent
underground obstructions, and groundconditions is recommended
Brief inconsistencies in depth may be
effectively overcome through the use of pitchreadings and calculations
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Interference Cont.Interference Cont. Drill locator is responsible for recognizing the
limitations of the equipment and
inconsistencies in readings If problems arise, the bore should be stoppeduntil identified and corrected
Should walk the bore path with the receiver onprior to boring operators to assess potentialinterferences
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Active InterferenceActive Interference
Can cause the following:
Erratic signal strength and depth readings
Loss of pitch and roll data
Inaccurate receiver calibration, leading to depth
errors
May be caused by anything that emits a signal or
generate its own magnetic field
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Examples of ActiveExamples of Active
InterferenceInterference Buried power lines
Traffic light power loops
Microwave towers
Invisible dog fences
Airport landing systems
Security systems
Fiber line traces
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Passive InterferencePassive Interference
Can cause the following:
Depth may appear greater than they actually are
All information may be blocked Drill head position may be incorrect
May be caused by anything that blocks, absorbs,
or distorts a magnetic field
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Examples of PassiveExamples of Passive
InterferenceInterference Metals fences
Re-bar in concrete
Electronic ignitions from cars
Buried metal
Salt water
Military operations
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Walkover Tracking SystemsWalkover Tracking SystemsConsists of three main components:
Transmitter (beacon or sonde)
Hand held receiver
Optional remote monitor
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TransmitterTransmitter
Emits a continuous magnetic signal at a
predetermined frequency
Ability to overcome interference is
related to its frequency and signal
strength
Available for depths up to 140 ft.
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ReceiverReceiver
Displays signals sent by
the transmitter in numeric
or graphic form Depth (ft. or m)
Roll or clock position of the
steering face or bent sub
Pitch (% of slope ordegrees)
Accuracy ranges of2%
to 5% of depth
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Remote MonitorRemote Monitor
Not essential to the drillingoperation
However, reduces drilling
time by providing the drilloperator with informationrequired to position andinterpret the reaction of thedrill head to the steering and
drilling conditions Some provide a graphical
representation of theprogression of the bore
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Bore Mapping SystemsBore Mapping Systems
Built into the remote display of walkoverlocating systems and stores:
Entry and exit locations and angles
Depth and pitch Bend radius
Alignment
Topographical (surface) elevations
Known surface and subsurface obstacles Transmitter temperature and battery status
Time between data entries
Drill pipe number
Drill head location
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As-As-BuiltsBuilts/Operator Logs/Operator Logs
HDD Contractor is responsible formarking the plans to indicate any and allvertical and horizontal deviations between
the design and actual bore Operator logbook should be maintained
and updated daily by the Drill Locator orSuperintendent and should include
Pipe number, depth, pitch, steeringcommands, and notes
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Home to Target SystemsHome to Target Systems
Enables the drill locator to program the
receiver to direct the transmitter to aspecified location at a given pitch
Beneficial in situations where the drill locator
is unable to physically track the progress of
the bore from the drill head
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DESIGN OF DRILLINGDESIGN OF DRILLINGFLUIDSFLUIDSDr. Samuel T. Ariaratnam, Ph.D.,
P.Eng
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